Ion beam treatment of workpieces such as silicon wafers for manufacture of semiconductor material is well-known in the prior art. Charged ions are created and accelerated to a specific velocity and caused to impinge upon a workpiece such as a silicon wafer. The prior art techniques for doping silicon wafers to produce semiconductor material are broadly divided into two classes of implanters.
High dose implanters typically use an ion source and focusing components for directing a high energy ion beam along a specified travel path. At an implant zone or station, the workpiece to be implanted is mechanically moved through the high energy ion beam in a controlled fashion to achieve uniform ion beam treatment of the workpiece. A U.S. prior art patent assigned to the Eaton Corporation which discloses and describes such a high energy ion implantation system is U.S. Pat. No. 4,234,797 to Ryding. This patent is incorporated herein by reference.
A second broad class of ion implantation systems use less intense ion beams which can be controllably deflected away from an initial trajectory to impinge upon different zones or areas at an implantation station. This type of lower intensity system also includes an ion beam source and focusing components for directing an ion beam along a specified trajectory. Along this trajectory, however, are positioned electric field creating electrodes which are energized in a controlled manner to deflect the ion beam away from the initial trajectory to the workpiece, typically a silicon wafer used in semiconductor manufacture. By controlling the voltage on the scanning electrodes, a uniform pattern of ion doping of the silicon wafer can be achieved. A representative U.S. patent disclosing a low energy ion implantation system is disclosed in U.S. Pat. No. 4,736,107 to Myron which is also assigned to the Eaton Corporation and is incorporated herein by reference.
Each of the two broad classes of ion implantation systems have advantages and disadvantages. The high current ion beam implantation technique has generally resulted in reduced wafer throughput and required large, costly wafer handling stations to move the wafer through the ion beam.
Deflection scanning systems used with lower current ion beam implantation have advantages in size and simplicity but cannot be used with high currents because the deflecting electric field results in beam deneutralization and consequent beam blow-up. They also suffer a disadvantage due to the varying angle of beam incidence the ions impinge upon the wafer. This varying angle of incidence is due to the electrode scanning of the ion beam side to side across the surface of the silicon wafer.